Technical Field
The present invention relates to a method for feeding electric power of at least one wind power installation or of a wind farm into an electric supply system. Moreover, the present invention relates to a wind power installation for feeding electric energy into an electric supply system and it relates to a wind farm, which comprises a plurality of wind power installations, for feeding electric energy into an electric supply system.
Description of the Related Art
A wind power installation is shown schematically in FIG. 1 and a wind farm is shown schematically in FIG. 2.
Wind power installations are generally known and, today, primarily serve the purpose of feeding into an electric supply system. In so doing, the wind power installation adjusts the current being fed in according to frequency and phase and taking into account the corresponding voltage on the electric supply system. This is a basic requirement, which must be satisfied in any case, and which is satisfied by known wind power installations. The same applies to a wind farm having a plurality of wind power installations, which jointly feed into an electric supply system by means of a joint point of common coupling (PCC). In this case, the wind farm feeds into the electric supply system.
It was recognized some time ago that it may not only be desirable to feed in as much electric power as possible into the supply grid with the wind power installation or the wind farm respectively, which supply grid will hereinafter be referred to as the grid for the sake of simplicity, but that it may also be desirable to use the wind power installation or the wind farm to support the grid. Corresponding proposals for solutions are described in patent applications U.S. Pat. Nos. 6,784,564, 6,891,281, 6,965,174 and 7,462,946. These applications already suggest that the power being fed in or the current being fed in be modified according to the magnitude and/or type thereof, as a function of a voltage or a frequency in the supply grid, in order to support the supply grid.
These days, the situation in many countries is such that wind power installations make up an ever increasing proportion of the total output in a supply grid. As a result, there is an increased need to support the grid by means of wind power installations. The dominance, and therefore the influence of the wind power installations in the grid is also increasing. Grid support by means of the wind power installations or wind farms in the grid can also be correspondingly effective.